Radon

An Update on Thoron Exposure in Canada with Simultaneous ²²²Rn and ²²⁰Rn Measurements in Fredericton and Halifax

Health Canada is committed to the development and implementation of an effective radon program designed to reduce lung cancer incidence by increasing public awareness of risk, and promoting testing and action to reduce exposure. Naturally occurring radon gas in indoor air is recognized as the second leading cause of lung cancer after tobacco smoking. Radon-222 (radon gas) and radon-220 (thoron gas) are the most common isotopes of radon. While extensive radon surveys have been conducted, data on indoor thoron is very limited. In this study, Health Canada used RADUET type detectors to measure the levels of radon and thoron in the cities of Fredericton and Halifax. Detectors were deployed in 45 homes in Fredericton and 65 homes in Halifax for a period of 3 months. Analysis of the radon results showed an average of 138 Becquerel’s/meter³ (Bq/m³) in Fredericton and 259 Bq/m³ in Halifax. Based these results, it was estimated that 18% of Fredericton homes and 32% of Halifax homes could have radon concentrations above the Canadian indoor radon guideline of 200 Bq/m³. Analysis of the thoron results showed an average thoron concentration of 203 Bq/m³ in Fredericton and 50 Bq/m³ in Halifax. Similar to previous thoron studies in Canada, no clear association between radon and thoron concentrations was observed.

The results of this study, combined with the data from limited thoron measurements previously completed by Health Canada, indicate that thoron contributes approximately 8% of the radiation dose due to indoor radon exposure in Canada. Health Canada recognizes that due to the limited sample size, this estimation is preliminary. To better assess thoron exposure in Canada and the risk it poses to the Canadian population, more extensive radon/thoron measurements will be required. Results of the research have been published in the Journal of Radiation Protection Dosimetry, 2011 Nov;147(4):541-7.

Assessment of Radon Equilibrium Factor from Distribution Parameters of Simultaneous Radon and Radon Progeny Measurements

Radon is a naturally occurring radioactive gas generated by the decay of uranium-bearing minerals in rocks and soils.  It is the most important contributor to human exposure from natural radioactive sources.  As it decays, radon gas produces radioactive decay products (also referred to as radon progeny) that form solids which can be inhaled and lodge in lung tissue.  These solids pose a potentially greater health risk than gas when they are airborne.   Health Canada has a mandate to promote and protect the health of Canadians by assessing and managing the risks posed by radiation exposure (including radon) in living, working and recreational environments.  While a great deal of data is available on indoor radon gas concentrations, direct measurements of radon progeny concentrations are limited.  Instead, concentrations are often estimated from direct measurements of radon gas using a mathematical formula that takes into account an estimate of the concentration of radon progeny that are airborne versus the amount that is trapped on surfaces, and thus harmless, represented by the equilibrium factor F.  In this study, Health Canada revisited a radon and radon progeny survey carried out in the 1970s in 19 Canadian cities. The average F factor assessed from this survey in 12,576 houses is 0.54.  The current assessment may indicate that the typical F value of 0.4, recommended by the United Nations Scientific Committee on the Effects of Atomic Radiation and the International Commission on Radiological Protection, could lead to a downward bias in the estimation of radon doses to the lung.  Application of this information will be used to inform risk assessments on radon exposure measurements.  The results of this research are published in Radiation Environmental Biophysics (2011 Nov), 50(4):597-601. Epub 2011 Jun 18.

Radon Exhalation from Building Materials for Decorative Use

Long-term exposure to elevated radon concentrations in indoor air can result in an increased risk of developing lung cancer. Although the radon gas in a home comes mainly from the soil and rocks under it, building materials can also give off or “exhale” radon. Health Canada undertook this study to obtain a better understanding of the nature and extent to which various building materials release radon, and the conditions under which such releases pose risks to human health. The exhalation rate of common building materials (porcelain, marble, ceramic, slate and granite) were measured and analyzed for potential health impacts. These impacts were based upon various factors including quantity of the product and existing environment/ventilation conditions.  This information was used to calculate the radon concentrations in air for three different scenarios: a kitchen containing a granite countertop; a room with an entire floor covered in granite tiles; and a warehouse containing 300 slabs of granite with common ventilation. For the household use, granite with the highest radon exhalation rate observed in this study was used.  Both of the household use scenarios produced radon concentrations levels well below the Canadian Radon Guideline of 200 becquerel per meter cubed (Bq/m³), with 3.6 Bq/m³ for the kitchen and 18 Bq/m³ for the tiled floor.  The warehouse scenario was also below the Canadian Radon Guideline level; however, if radon exhalation rates are very high and the air exchange is low, workers could be subjected to significant occupational exposure from radon in the air. The results of this study showed that while slate and granite had higher average radon exhalation rates than the other decorative materials tested, building materials used in home decoration do not make a significant contribution to indoor radon levels provided there is adequate air exchange.  Health Canada will use the results of this study to support further risk assessments and risk management issues related to radon.  For more information on this study or on radon, in general, please contact: Radon@hc-sc.gc.ca. The results of this research are found in the Journal for Environmental Radioactivity, 101(4): 317-322.